I don't know if RV are covered by any specific laws in the USA - however in the UK I'm aware that there are some legal or restrictive laws in place to try and prevent people using ultra wide angle photos for promotional purposes to make small homes look bigger than they actually are.
The RV world might be similar, further I suspect most producers don't want to miss-represent their product to potential buyers.
However they are very small and compact places and with crop sensor I've a feeling that a 70-24mm might be a bit long in some cases. A 17-40mm might be a more suitable option for such photos, giving you a big wider field of view to work with at the 17mm end. Add in a good tripod and if you need a wider shot you can always pan and stitch in editing.
From there you'll need editing software as wider angle shots will have some distortion - from what I know many processing options will have these - Lightroom has this feature and so does DxO's own processing software. Lightroom would probably be the easier option to the two to pick up (plus increased numbers of articles online) though along side that you might also need a regular editing package (Photoshop CS5 is the ideal though Elements 10 will do most of what you are likely to need).