Honestly it all about compromise. You can take the middle ground approch and do the research get the enclosure ready and just continue to talk to him about it (not nagging) and eventually he will probably agree. I let my SO park his chevy 350 on a motor stand in the living room during the 3 months of hurricanes a few years back so he owes me big time!

Have you asked him what his reasons are for not wanting to get one?