I had a couple of "thinks" on coatings. Specifically; It's probably worth testing out some of the various Water
Based paints on a few scraps of netting. And by testing, I mean that said test pieces should be; coated, & then put into an area/situation where they are repeatedly subject to stress flexing (the load induced type), & lots & lots of UV exposure.
Then, once your testing yields some useful feedback, you could do a Heavy Duty laundering of your (in place) uncoated nets. And then paint
them with a few coats of "X". Based on your coating trial test results.
The thinking behind the water
idea, is to remove as much in the way of solvents & chemicals, as is possible. Which go onto the nets. Or as much as you reasonably can, anyway.
Maybe look at trying out some of the Latex paints, for their inherent flexibility. Though I wouldn't cross a WR LPU off the list automatically. Like, say the one made by System Three Resins, or similar.
Also, have you given any thought to sewing some (wide'ish) webbing to the perimeter of your nets? As I'm thinking that if you were to heavily affix some 2" (50mm) wide webbing to their edges. Then it could assist in preventing (much of) the point loading on the individual strands of the netting. Particularly where it meets the boat/lacing fixtures.
Or, as a plan B, do the same type of thing, but with, say, a 4" (100mm) wide perimeter of canvas
affixed to the nets (on both sides, top & bottom).
Much like the extra cloth which goes onto a sail at the clew, & around reef points. Albeit, I know that the workability/viability of such depends on the attachment points built into your boat.
Also, once you're done building your new nets, & are happy with the results: If you'd be so kind as to post; what you looked at hard, & or tried. In terms of both: Kinds of netting, and also coatings. I know that I, & likely lots of other folks, would be very appreciative of learning
of such information.
That info, plus anything else relevent, which you discover on your quest.
PS: Another idea on where to find cheap
netting might be to contact the netting manufacturers directly. And ask them who, amongst their distributors, might give you the best deal, & or, who routinely have some appropriately sized scraps around.
That, or you might get really lucky, & find a manufacturer who has some "factory 2nd's" on hand; cheap
or even free (but for the price
of shipping). Especially as you don't need much, nor for it to be full on extreme duty stuff. Thus, a 2nd or off cut, might serve just fine.