Modifications for long term travel

Since I didn't find anything on a search, I'll ask; has anyone with an older unit added features and ammenities of the newer rigs? I'm looking at adding a washer/dryer and full sized fridge to the garage, directly behind the living room wall. The reason is we plan on pulling for a year with the kids; we could get something more suited for the purpose, but may get stuck with serious issues (or none at all). Considering that our rig also has issues, but is paid for, and will have at least a decade note on the other, it's a gamble we're not willing to take. The money will spent on a better tow rig.

I'm trying to get some ideas about install costs (plumbing and electrical) and actually installing them for RV use, I.E. how to mount them? We will also be adding a set of bunk beds back there and a large wardrobe for the kids. Other mods; removing the u dinette and installing a table and reclining sofa in it's place, removing the small RV fridge and having a cabinet built, along with extending the counter space. Anyone ever take on that challenge themselves and care to give some pointers? Thanks.