renting to own?

my fiance and i looked at a mobile home yesterday to possibly buy, but it's going to take awhile for us to get a mortgage, because we've got some credit problems we have to take care of first. the mobile home owner (who's family is friends with my fiance's family) said he'd consider letting us rent to own until we can get our own mortgage. (he's in a hurry to sell so he can move up north where his wife and kids are). he wants to sell it just for the ammount he owes for it. is there anything we should know before we go through with this?