Everything I learned about varnishing was from the manual, YouTube videos, and Ken (faithie999) so your mileage may vary. I completed varnishing all inside surfaces and my galley module but I haven’t done the outer cabin yet. I used a 4″ foam roller to apply, a brush to tip (see below), and a foam brush to apply varnish in nooks and crannies (then tipped with the brush).
I couldn’t find the brush Ken recommended so I went with a Purdy Syntox brush which is a combination of Chinex/Nylon bristles. Lowes stocks it next to the varnish and poly, not with the normal paint brushes. However I’ve since seen Red Tree brushes on Amazon if you have the time to order. https://www.lowes.com/pd/Purdy-Syntox-Nylon-Flat-Sash-Paint-Brush-Common-2-in-Actual-2-in/999972050
I already had a set of foam rollers that I’ve been using and I’m incredibly happy with them. I wish I had them when I was doing the epoxy work. https://smile.amazon.com/gp/product/B005MI3RX2/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1
The 3M pads the manual (and Ken) recommends: https://smile.amazon.com/gp/product/B0002SQYF0/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1
When I varnished the galley module I only used a vacuum and then denatured alcohol to clean it up but I got a lot of bumps in the finish. I then purchased some tack cloths and I think it makes a huge difference. For about $1 each from HD or online, they are totally worth it. I get about 2 uses out of one before I toss it. https://smile.amazon.com/gp/product/B000CINDQS/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1
Another tip from Ken is to put plastic wrap in the can up against the top surface of the varnish when you’re done for the day. Otherwise you get a thick skin on top (like pudding) that is just wasted varnish. When pouring the varnish out into a disposable 4″ roller pan I run it through the cheap mesh paint strainers you can get near the paint sprayers at a big box store. They run about 3 for a $1.
From a temperature point of view, I found that if my shop was hot, everything worked fine but the varnish would get tacky really quickly so it was hard to maintain a wet edge. I would recommend rolling and tipping in very small areas so you can tip before it gets tacky and maintain the wet edge. More than a couple square feet before tipping and you’re going to run into problems with brush or start/stop marks.
Like Ken, I wasn’t willing to empty my garage or shop to clean it. I vacuumed the floors and any top surfaces I could get to. I also try not to sand and varnish on the same day. My routine is usually sand, vacuum, alcohol wipe down. Next day, tack cloth, varnish. Repeat. That gives a day for dust blown around from sanding and vacuuming to settle and the tack cloth picks it up quickly. So far I don’t feel like I’ve had a huge issue with dust in the finish but I have strategically allowed hundreds of spiders to form natural dust control webs around my shop.
Being a guy with hairy arms I also wear a clean long sleeve shirt which I feel like helps keep down the stray hairs especially when I accidentally bump a tacky varnished surface. If it fit with the respirator I might consider a beard net too.
Overall I’m actually enjoying the varnishing process. It might be the fumes getting to my head but I find it much easier to work with than epoxy and the immediate change from dull, gray, sanded epoxy to beautiful glossy wood is very rewarding.
-mike