The first step in getting a contractor to apply Spray Foam to TTs / 5ers underbelly is to obtain financial estimates. Many companies will provide "over the phone" estimates (based on provided measurements - like 10ft x 25 ft x 3.5" thick) and others need to see your situation first. Some companies can visit your TT/5er using their Mobile truck/trailer and others ask you to bring your tt/5er to their shop (to be inspected withih their well lighted Spray Foam booths).
To obtain initial financial estimates, simply use Google Search - to find the Spray Faom companies within your area. For example (for your Austin Texas region), surf the many URLs within: http://www.google.ca/#hl=en&safe=off...f023fa88c5b3eb
If into DIY Spray kits, surf http://www.rhhfoamsystems.com/
When using DIY kits, remember to order 20% more square footage - for "learning curve" waste. From my experience, "contractor grade" Spray Foam (applied by a certified contractor) is much better approach. And, remember to use Close Cell - 2 lbs. 1 lbs is too light (fluffy) and Open Cell cannot take water exposure. For TTs/5ers/RVs, only use CC - 2 lbs Spray Foam.
Note: Do shop around because estimates do "dramatically" vary. When obtaining cost estimates for my TT, the cost range was double - from different contractors. And, they used a product that wasn't very good either. Like any consumer purchase items, do shop wisely (for price and product quality).
If you feel "applying" spray foam is within your wallet depth, the next step is to prepare your TTs / 5ers underbelly. Simply remove existing underbelly panels, fabric materials and existing Fiber Glass insulation. And, prepare the underside for spraying. The more you can prepare, they less cost they charge you. Like paining a vehicle, the master sprayer guy comes in, sprays and leaves. You don't want to pay an expensive master painter to waste time on incorrect prep work. Same approach applies to spray foaming a TT (or insides of a refridgeration truck).
For initial preparation tasks of existing insulation removals, surf:
With underside wood floor exposed, Re-route all under belly wires into nice straight and smooth 90 degree corner runs. And, install all wiring within over sized plastic loom as well. Wire loom can be fastened to under floor wood using galvanized steel strapping and 1/2" wood screws. If you need to replace a future wire, simply re-fish the wire into to over sized plastic loom. Push fiberglass between the tanks under floor gaps as well. If spray foam is applied within the tank / floor gap, the foam will expand and press the tanks down. Thus, warping the top of the tank or could break its holding straps. Simply push fiber glass insulation between tank and its gap. Or, apply blockage material in this gap area.
Remember to apply barrier cover under the tubs gooseneck as well. Thus, reducing spray foam getting into the underside of the tub. For example: http://i178.photobucket.com/albums/w...e/100_2056.jpg
Then, apply plastic sheets around items that cannot be sprayed. For example, tank valves, slide out gears, slide out motors, etc. etc. And, apply pastic to reduce over spray on unwanted areas as well. After spray foam, simply remove this plastic.
If you plan to install future wiring (like 12V brake wiring replacement) or 12V wiring for additional lighting, install a 3/4" PVC pipe with split out boxes every 10 feet. When you plan to install future wiring, simply fish the wiring into this pipe.
The above is how I replaced the factory fiber glass insulation with Contractor Grade Spray Foam under our 2006 Jayco. For our next TT / 5er, I'd do this upgrade again - without hesitation.
Good luck in your TT/5er insulation upgrades...