As you can see the panel is taped with blue painters tape. I do that to protect my hand oils and other art materials from getting on the surface before I decide about the choice of color or if I should stain them or leave them natural.
I only bring the blue tape up to the top panel edge so that can be painted with the brown acrylics. And as you can see I get a bit happy with it and make a mess done the side of the tape. Well that's why it's there. After the paint soaks in, I give the top and side edge two coats of Polymer medium.
I also give the collage that I created on the 140lb watercolor paper two coats of polymer medium on it's back side. Be aware it may look like its curling up but it will be fine when you tack it down.
Hope this helps answer the few questions I have had about it. No reason why you can't just collage on the panel...I'm doing that with a large one from Ampersand I've just coated the surface with two coats of the polymer...Yes I've got the polymer jar strapped to the art utility belt I wear... all day. When you buy it by the gallon you use it on everything...Oh when I finish pull the blue tape off and then I finish with Satin varnish on wood sides and top. You can give it two coats too...dries fast cause the first layer soaks in really quick like.