Packpack DIY frame-finishing question

Yesterday, I finally found a budget-level, almost fully "clamshell"-design backpack for short 4x5 outings. It is a Targus model, about $35, at BestBuy, where I had gone to use a $25 gift certificate. I have built an internal frame for it out of 1/4" poplar; I haven;t quite decided on how to complete the top shelf area. I have some clear, water-base polyurethane and wonder about using it to finish the wood, though I think it might be wise to also, or instead, to pad the frame insides with felt.

You hikers will already know I'm not one, and I'll have to see how comfortable, or not, this is for me. But as you can see, my load is small. I have only two lenses, and this will accommodate them, 4 holders, Pentax V spot meter, loupe, and misc.

I post images here for any who might benefit. The black bundle on top of the camera is my dark cloth -- an XXL black T-shirt. The meter pocket is the outside back one; I couldn't fit both it and the lenses inside.

Any problem with using the poly (outgassing)? How long should I let it cure if it is an issue?

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PM Drew Wiley-if anybody knows, he does.

Oh, I just spotted this. Most acrylic polyurethanes simply dry. Just allow a few extra days after seemingly dry for a margin of error - a week or so should be ample. It depends on the humidity.

Much obliged, as always.

Before I apply poly, I typically wipe the wood down with a damp cloth and let it dry. This causes it to burr up. You can then sand it with 220 or 300 grit, and THEN apply the poly - which you can just wipe on with a clean rag. This gives you a smoother, snag-free finish. Typically, I apply the poly, wait a couple hours, and apply a second coat.

Before doing any of this, I do recommend sanding the corners so they are not so sharp. This will help when you later apply the poly.

I'm impressed by building a custom wood frame. I hope this isn't taken as critical:
- A foam insert with dividers would likely be protective enough. However, many non-hiking backpacks do not have enough structure to be comfortable to carry, so the frame may help there.
- You definitely should have some padding between the items and the frame. Not sure if you planned to wrap each item individually before putting them in their compartments. You could probably get away with just a layer of felt for the things like camera and filters, but the lenses should be in either padded compartments or wrapped in something (a lens wrap, bubble wrap, etc) and not allowed to move around within their compartments.

reddesert, yes; lenses will be wrapped; camera compartment padded or I'll wrap my cloth around it.

If you find it too stiff or uncomfortable to walk with there are padded ICUs that would likely fit and allow more flexibility over time. Shimoda makes some really nice ones but I have found unknown brands on Amazon or Ebay that work just as well.

esearing, thanks for the tip. Unfortunately, the only out-spelling of your acronym that comes to mind is Intensive Care Unit, and a padded one sounds like the fabled psychiatric type. While there are those who occasionally raise an eyebrow with regard to the sanity of pursuing large format photography, perhaps you were indicating something else, and I'd love to know what.

google is your friend - Independent Core Units. OR Internal Core Units. They do the same thing as your plywood fabrication. Examples https://www.bhphotovideo.com/c/searc...a%20ICU&sts=ma

Esearing, thanks. The signal difference between ICUs and DIYs in this instance was price. I'm a miserable excuse for a builder, and you can just imagine how many nails bent or went in sideways, much to my exasperation -- though I should be used to this by now.

The backpack for me is a convenience that I don't expect to need often, and not for any serious hiking. Otherwise a long-term investment would have to be considered.

Conventional EVA foam padding adds a lot of redundant extra weight to a pack. It might be OK for little shoulder bags, but it is not only linty, but doesn't offer anything which can't be improvised with basic bubble packing and some fomecore board dividers at considerably less weight. I use Gatorboard for water resistance and extra strength; the perimeter can be a stronger plastic like a polyethylene wastebasket. There are all kinds of ways to do it. However, I do this in conjunction with seriously built external frame packs capable of hauling serious gear weights if needed.