Use caulk to seal or...?

I have a DIY growbox made from two big plastic storage bins and I just cut out a square for a little PC fan. The cut-out wasn't to exact size, though, and there's open space around the fan (it still fits really, really snug).

I was wondering what I should use to fill the gaps? I was thinking caulk but then read that it doesn't work too well with plastic...

Please help

I used silicon to seal my closet but I let it air out for about 8-9 days before I got busy and I havent had any probs but that was my very first grow experience so there may be sumthing wrong with silicon.

I have several different kinds of caulk and a silicon mix is one of them - did you use it on plastic? I'm not really worried about the fumes (unless they'd activate under heat?) and it doesn't seem like you had any problems.

I'm just wondering if it is the best thing to use for plastic, especially since it says against it on the bottle. I can't think of any other kind of sealant/adhesive/fill, though...

No I didnt use it on any plastic, dunno if that will make too much of a difference since Ive used silicon on plastic in several boat rebuilds.