It seems like you're putting a lot of thought into this and it's worrying you a bit that you may get caught. It seems unlikely that you will but you can bet the one time you go down their to burn one down someone will turn up. Only you really know whether it's a risk you're willing to take. Maybe sneak in there and hang around for 10 minutes just to get a feel for hte place and to relax, if you reckon you're not gonna be bothered by anything and you're sure that paranoia won't set in once you're high then go for it.