Wash Techniques

I like Future for my sealing layer between enamel base coat and any washes. That stuff is pretty much impervious to most thinners. Also you may want to try a soft  natural sable bristle paint brush rather than a q-tip for clean up. The q-tip may exert too much pressure and friction.

Agree with stikpusher, use a brush, not a q-tip.

I'm also wondering what is in the thinner you got at the hardware store. All thinners are not the same (read the label). I use odorless mineral spirits and oil paint for my washes and have never had it eat through any acrylic paint. Plain old mineral spirits may not work with enamel paint, so you may have to experiment with different thinners.

Chris

Get a set of decent but inexpensive brushes 40% off coupons at hobby lobby and michaels. I too use odorless mineral spirits found in same aisle as artist oils. I paint with acrylics and wash with acrylics and artist oils. I never seal the paint and have never has a problem with the basecoat being damaged and i tend to be aggressive with my washes.

Trying new techniques is very much a trial and error process. You may want to go find and old build of yours to use a "crash test dummy". Any and every new techniqe for finishing that you may want to try such as: pre shading, post shading, washes, dry brushing, dot filters, pastels, etc. can be tried on this old build without worrying about ruining a new build, as you had happen here. A way to find out what works for you and what does not work for you as well.

Use odorless mineral spirits as a thinner.

I use Flory washes over lacquer gloss, works like a charm.

I spray a Tamiya acrylic and let it dry, then add my wash of artist oils thinned with a generous amount of Turpenoid. This works every time and the wash can be controlled by the mixture, I  prefer it slightly heavier for panel lines etc.