I have three questions:

1 Getting 110V power that is in the that space behind the 12V DC.
2 Where is fuse for the cruse control.
3 I need to order a windshield washer fluid container for a "85 P30.

There is so much variation among Barth coaches it is hard to say where the fuse for cruise control would be. There were several different cruise controls used, all aftermarket.

Normally it would be powered by an aux tapped into the main fuse block on the front firewall. There is likely an inline fuse in that power lead.

As for 110v are you referring to the "space" for the TV or where? Most coaches with a TV in front had both 12V and 110V.
The power feeds often had a relay to cut out the TV while underway.

As for washer tank, again there is much variation. Check google images see if you find a match. You can prob adapt almost any tank to work with mods.

good luck

Hey John,
I've been looking for one for my 86 since I got it with no luck yet. I'm guessing yours is pretty much a rectangle with a lid and 2 pumps right? Let me know if you come up with something. The two pumps is the hiccup.

pretty sure our cruise fuse was under dash, drivers side, above where your left foot would be when sitting in drivers seat. Fun to get to. May want to do some stretching before you go there.
Tere