Lender is taking an RV park which has two mobile homes on the property. The mobile homes are attached to the property but still are titled, not surrendered to be considered 'real property'. If lender does not take the mobile homes as collateral and file a lien on the titles, takes only the land itself, do we have to require flood insurance?

No security interest in the buildings = no flood insurance.

Thank you!

Does the same apply to stick built homes not being taken as collateral on a loan?

Sure - if you can figure out how to write your deed of trust or mortgage to exclude any improvements on the property, keeping in mind that you have to foreclose, then you will have a property in OREO that has buildings on it that you do not own. It may be sort of hard to sell I would think.