This is for a rear auxilliary tank for a rally bike.  I have a plug ready (which I can change) but before I mould form it I could really do with some help in terms of joining the two halves once made.  The only hole in the tank when it's joined is just a fuel filler ie it's small, so whilst I can get in there with carbon tape and a "brush on a stick" it's not  ideal.  Also, the external side: whilst the tank is going to be painted what would you guys suggest is the best method for an external join?

We're talking infusion here rather than pre preg so I cant use a bladder or anything like that.  Could really do with some wisdom please.