You might find this buyers checklist of use. Fiberglass RV - Document Center - Buyers Check List
TWO Berner Sunnenhund is a LOT of floor space :-) In a 13 ft. you might have to consider you take the bunks and give them the bed!
Here is a link to the Fiberglass RV rally
map, you might want to consider hitting one of these. Open house time is common at a rally
and most participants would be happy to show you their rigs. Good way to see lots of brands and models to get a clear idea of what will work for you. 2015 Rally Map on Google Maps
I do see a May rally
over in Indiana.
The bunk model of 13 ft. the bunk is convertible between a couch or bunk bed. If you dogs will both sleep or lie down on the 6 foot of couch with the top bunk up (makes a cave sort of) then you can use the top bunk as a shelf for gear while the dogs take the bottom bunk. Floor wise 13 ft. only has about 5 ft. of floor. A 40 lb. Standard Schnauzer takes about 1/2 of it. Or stretches out until she does. My Floor!
Also need to consider what the tow vehicle can handle in terms of rated towing weight
in picking a camper. This list of trailer weights collected at rallies may prove useful. Trailer Weights in the Real World
Some weather can make AC pretty much required for the dogs comfort. AC adds weight
and sometimes takes up storage space (Some Scamps have them in closet/cupboard) Or on roof make the camper taller which may not fit in garage or carport. Bathroom will be a lot of floor space to give up when the 4 of you are in there so that might impact the size camper that will work well for you.
I'm sure some big dog owners will weigh in soon, we have a lot of dog owning members that camp or travel with their dog, couple of cat owners too now that I think about it.
Good luck in your search and welcome!