I was struggling with that until I spoke to an IA friend of mine the other day. He builds a lot of ultralight/light sport planes. He said "big chunk of PVC pipe, cap on both ends and shake.

Duh. Wish I thought of that. To get the timing right, thorough rinse etc I will have my son help me. Do the etch and rinse on all the pieces, then rinse out the PVC really well, then move to Alodine - and dare I say "rinse, repeat".

Before that idea came along I was going to modify the crate that my spars are in with a big plastic sheet and make a tub out of it. The PVC will produce a more uniform product.

If you're going to do the outside by hand dipping then you could use the tennis ball trick just like you'd have to do with primer for the inside.