It it not entirely clear what your question is.Taking a shot in the dark, Unrelated Business Income Tax (UBIT) applies whenever a tax exempt entity (Solo 401k, IRA, or any other type of non-profit) engages in a trade or business on a regular or repeated basis. refer to IRS Publicaton 598.Income derived from passive investments such as rent from real property, interest, dividends and royalties is not subject to such taxation.UBIT was created by congress long before IRA and 401k plans existed, to prevent tax-exempt entities from driving taxpaying businesses out of business.  

Reason is each category of property , at least to me, has different set of challenges, opportunities and costs so the numbers are different. 

Below are some quick links to get engaged on this site. http://www.biggerpockets.com/startherehttp://www.biggerpockets.com/meetSetting up Keyword AlertsHow to Use @Mentions on BiggerPocketshttps://www.biggerpockets.com/ruleshttps://www.biggerpockets.com/invitesREI books suggested by BPershttp://www.biggerpockets.com/renewsblog/2013/04/14/best-real-estate-books/?

Below are some quick links to get engaged on this site. http://www.biggerpockets.com/startherehttp://www.biggerpockets.com/meetSetting up Keyword AlertsHow to Use @Mentions on BiggerPocketshttps://www.biggerpockets.com/ruleshttps://www.biggerpockets.com/invitesREI books suggested by BPershttp://www.biggerpockets.com/renewsblog/2013/04/14/best-real-estate-books/?

An RV being mobile seems to present additional challenges in this scenario. 

Equity is the meat.It's important to remember that you're either trying to buy equity or cash flow at a discount.A significant challenge of trying to become an investor, in the beginning, is that we become attached to each of the few leads that are generated and try to squeeze every ounce of possibility out a very opportunity.

Below are some quick links to get engaged on this site. http://www.biggerpockets.com/startherehttp://www.biggerpockets.com/meetSetting up Keyword AlertsHow to Use @Mentions on BiggerPocketshttps://www.biggerpockets.com/ruleshttps://www.biggerpockets.com/invitesREI books suggested by BPershttp://www.biggerpockets.com/renewsblog/2013/04/14/best-real-estate-books/?

This past week we had some delays and challenges.  

While you wait for connection with a NYC broker, below are some links to get you engaged.

This thread is really reinforcing the challenges of starting out in California.