With any project like this, the key is PICTURES!!! PICTURES!!! PICTURES!!!
(Did I make my point?:B)
The thermostat should be similar to what you have in your house, but at worst, you could pay a bit more, and get one from an RV Center...if you are trying to restore the RV to "original".
If you are just trying to make it liveable, a lot of the small things won't matter to much.
As for the vent. Is there any sort of vent grill under the dinette bench? If you think that this would be a good place to have one, you may want to make that change part of your project. A lot will depend on the size of the RV, as well as the weather you plan on camping in. If you won't have much need for the furnace, this isn't going to matter much.
Personally, I'd keep it in place, and install a vent.
Good luck with the project...there are lots of folks here, who can help you along the way, but as I think I may have mentioned, PICTURES!!!:B
