There seems to be a few 10 year rule RV parks in southern CA and southwest. The great majority are not. For practical purposes, a well kept year 2000 motorhome is nearly indistinguishable from a 2005. In all my travels I have never been asked for registration or other documentation about age of my RV-including at 10 year rule parks. Nutshell: keep it nice and fib about the age.
Semi on topic-but not critical for 10 year rule. One thing which really ages RVs in my opinion is the way the plastic headlights yellow and become cloudy. Some beautiful rigs have that as their only cosmetic blemish-and it is a performance issue too. People have varying success with polishing the lenses but it generally lasts a while and they look great. Another option is to ID what common car/truck uses the same parts and search online for inexpensive replacements. Due to how common this problem is, cheaper sources are cropping up.