We replaced the carpet in our 78 Excella 31 last spring. Heres are some notes that may help you (If you havent dont yours installed already)
1. We used a thick pile residential grade carpet (and had no problems with doors etc opening)
2. The original carpet was used as a template. (cut the carpet upside down, with the original carpet on top of it + upside down for tracing)
3. Get a Professional carpet knife from Home Depot + LOTS of spare blades
4. Our carpet came in 10 ft width, so I just turned it sideways and had a seam in the middle of the trailer.
5. A regular heay duty staple gun with long staples (I think they were 1/2 inch) will work great.
6. Rent a carpet kicker to stretch the carpet. I ended up with a minor bump but eventually got rid of it.
7. I took back the left over pieces of carpet and cut 3 pieces asked the carpet outlet to "bind" the edges and we used them for area rugs / entrance rug. The carpet place did all the binding for 20 bucks !!! I used them in the dorrway, Lounge + Galley to save wear.
8. Installing the carpet took all about 6 hours and looks great, see pics.
I cant help re the doghouse on your 310, but all our carpet was installed to the "edge" of goucho etc and looks great. Thicker pile carpet allows for larger room for error and butts up nicely against things.