Progress report: 07 Freightliner build.
The truck mods are now (almost) complete. I spec'd out the longest frame available from Freightliner however,...the frame tails had to be extended 18" to accommodate a 33' body. This was relatively easy, as no mechanical extensions were necessary.
Mounting the Big Foot jacks required moving the (truck) battery box to the rear aprox one foot so the (front) jacks could be mounted directly behind the cab. Again this wasn't a problem, Freightliner actually left enough "extra" cable to make the move without cut/splice & extending anything. The Big Foot system uses four individual hydraulic pumps, one for each cylinder. After looking at the pump/resevoir units I finally figured out that they resemble marine lower unit lift pumps. This little bit of info may come in handy if one gives up on the road. Marine & boat places are usually easier to find than RV supply stores (also maybe less exsensive).
Anyhow,...we went with a frame mounted (aprox 42 gallon) propane tank which was set in behind the rear axle between the rails. This appears to be a reasonably safe location and also saves storage compartment space. We are down to extending the exhaust and cutting the opening in the rear of the cab.
The next step is to build the floor structure, walls & roof, set the completed "cage" on the truck frame, then continue construction with the body mated to the truck.
Hopefully we will have this phase complete in another couple of weeks. Photos to follow (eventually)

How do you access the fill on the propane tank? Is it exposed in the rear? Just curious

A remote fill is available that has a bleed orfice that lets you know when it's full (as used on most tanks). It spews vapor until near 80%, then it spits liquid.
I'm also using a Vena monitor system that provides constant read-out of fresh, black, grey, & propane levels, along with battery voltage. It reads "through the tank wall" so no holes need be drilled and,(obviously) the sensors don't get corroded, so they actually work! Hawk Engineering has them in stock.

cool, didn't know such an animal existed, our fill and bleed have to be accessed from the compartment, didin't know you could make them remote!

Can I ask where do you find information on building the "box"... I'm assuming there are rules of thumb much like building a house (16" o.c. etc). Thanks !

Sincerely, Bill

Bill, I don't know that there are any exact standards set out for the construction of a conversion shell. The RVIA (Recreational Vehicle Industry Association) does provide "codes" as in the commercial/residential building industry that governs construction, electrical, plumbing, etc,... from which most manufacturers adhere.
I visited several manufacturers in Elkhart Indiana, and one in Eastman Georgia, and got "somewhat" educated in how their conversions were built.
All (that were using steel tubing) used 16" centers in their wall construction. This makes sense as most demnensional building materials lend themselves to (even) division by 16". However, the floors & ceiling structure on some units used 2 foot spacing. This probably depends on the demensions of the steel being used.
Again, the conversion manufacturers that I observed, used 2"X 3" 11 guage for floor X-members (on 2 foot centers) and 2"X 2" sq tubing for ceilings (also on 2' centers).
You can learn a lot by touring some of the (Elkhart) production-line guys, especially Trendsetter & Showhauler.
When you draw out your floor plan just remember, you are working in sq inches, not sq feet and you need to make good use of every inch.

Bob,
I am also just starting a conversion and will fabricate my own box. I am a little nervous about these slideouts. Do you have any pictures of them or know where to get the components from? Also, how are you going to connect the truck to the box to ensure a tight seal?

I've "farmed out" the construction of the sq tubing structure as I don't have the space nor enough arms, legs, a-holes & elbows to do it myself. Besides, I figured it would take me 6 months to complete if I did attempt it. I would suggest you draw a very comprehensive & detailed plan of the structure prior to begin cutting & welding, I've found there is alot more complication there than meets the eye. Anyhow, to answer your questions: The slideout drive & support structures (there are at least 3 different types) all come from the Elkhart area. Jason at Hawk Engineering (who is doing the structure for my project) has ordered in the type that suspends the slide floor from the ends. It also supports the floor from the front and back on both ends.
The telescoping sq tube type only supports the slide from the outside edge of the floor so these generally require a roller in the middle.
I went with the ft-to-back support design as I'm installing granite tile flooring and have concerns with a roller possibly cracking the tile. Also this system uses a drive shaft off of a gear motor that inturn runs (2) screw jacks that move the structure in & out. The whole thing is supported from the sides of the opening, not underneath. The disadvantage (?)is that the slide floor is elevated above the main floor aprox 1 &3/4" (to the top of the floor covering). I'm not sure of the specific manufacturers (names) but I believe you could probably find them on the internet.
The seal (truck to motorhome body) we're using, is an accordian rubber with an aprox 3.5" cross section and has pinch weld grooves on both sides. It apparently comes in a large roll. Again, Jason is supplying this and I really don't know where he bought it.
I'll be back in Mo in a couple of weeks & attempt to get some info on this & the slide manufacturer.

Well,...the shell build is complete! From the exterior it looks like it's ready to live in,...from the inside it looks like a racketball court. Jason at Hawk Engineering did a class A+ job, everything that was specified in the contract was completed in a very professional manor.
Now the fun begins. I brought it home a week ago and (of course) had a 30 mph head wind all the way. Figured my fuel mileage and was pleasently suprised. Even with the head wind I got an even 8 mpg. Hopefully, when it gets broke in (and without a headwind) it'll do even better.
I think I've got a master plan finalized (?) that will map out the interior construction. Next week I'll begin installing awnings, roof AC's, TV antennas, solar panels, exterior wiring, etc. Then start insulating. I've decided to use 2" extruded foam in the walls and ceiling, then add additional 4" fiberglass in the roof between the drop ceiling and roof structure. Hopefully this will make it comfortable Summer and Winter.
I'll attempt to post updates as I progress. There is no doubt my "master plan" will end up being revised a hundred times in the next few months. Any suggestions or comments would be appreciated.

Hi could you post the address and phone of the body builder.

hager2780@msn.com