Finished the new version of the boiler unit for the tracker.
The mylar's a bit bumpier than I'd like, it's currently stuck with double sided tape but I'll try to source some spray on adhesive. You get the idea tho.
It actually holds together really well, the form is surprisingly solid for just four bits of card.
Just a bit of copper pipe squashed flat, painted black and sheathed in clear plastic. I've used metal epoxy to seal the ends as it's about the only stuff that will resist heat and ethanol.