A lot depends on how intent you are in a particular exit strategy. If you exit strategy is a McMansion in the hamptons, it will take a lot of money set aside. One of the things we love is the flexibility of the lifestyle. The RV is our fall back when the boat gets too much (or maybe we switch to a one level house boat). But if and when we give up the mobile lifestyle entirely, we will likely pick an inexpensive but nice area and pick up an apartment. $6-800/month should get us a comfortable 1 bedroom apartment with far more space that we currently live in.
In general terms, keep the RV to a modest percentage of you net worth. (Ie: if you are worth $10million, a $500k MH may be well within what you can afford to lose. If you are only worth $750k, a $500k MH is a crazy purchase.)