Several Items -
Sign on to the truck camper group on this site. Your rig is more a camper than a motorhome although the sleeper is bolted to the chassis instead of sliding into a bed. Lots of info on that group site.
On sealing - it looks like the framing surrounding your front window is likely to have openings to seal. Use some marine caulking to close up any wholes - advise that you first remove the parts to find out what lurks below.
Do lots of resarch before spending money. Enter your problem on YouTube and you will probably find an answer.
You bought a "home" and a motor vehicle. Research Dodge truck discussions to find a group is interested in your vehicle. Then rely on RV.net for the home area as you get to it. Right now, you can sleep in the overhead or on the floor if you drive to a camping area. Seems to me that you should get the vehicle portion into good shape before starting on the rear unit. If the vehicle is running and cleaned up a little, I suspect you can resale for what you have in it if the restoration seems too much. At minimum, you have a good work van as it is.
