They have no physical claim to the ground or stand, only their history there (which is significant).
Their clubrooms and 'official' no.1 pitch are actually across the road (North Park). They have actually played prem games there in the past and there were even rumours a couple of years ago they wanted to move the games back there.
The history they have at the Rec and the momentum the nimbys will take from this are the damaging factors. Unfortunately that might be enough to stop it.
To be frank, this is pathetically incompetent that Welnix didn't get these guys onside from day 1. I'm sure it wouldn't have been that hard - the rugby club were obviously on the fence considering they didn't come out opposed until now.