Hey, we have a low end 2004 and it isn't OLD!
We bought it as a 4 year old rental from a reputable dealer and have had no particular expenses in 5 years other than a set of tires which is a very big cost but an expected one. The trouble is you need to change tires every 5 to 7 years no matter how far they have travelled.
Our dealer made sure there were no leaks and that everything worked. Tried to sell me a useless warranty and failed to warn me the roof is not made to stand on. Fortunately I aways chat up the guys in the shop who really know stuff. Use planks when you go on the roof to check caulking.
Is that a Ford V8 or V10 with Triton engine? If so, you should be aware there can be expensive difficulties changing the spark plugs. I think the 2003 trouble is that they can break during removal. You could easily go another 25 k miles before doing that but if the dealer is in the mood to do a spark plug change for a flat hundred or two, I would sure go for it.
Be aware MHs use a lot of fuel, but it is worth it - a wonderful way to holiday.