Yep, cutting and plastic welding the case would be a mess, and toxic for me, so I'm holding out for a 6V battery. We're smoked in again last night and this AM from wildfires so my health and enthusiasm is ebbing.
I'm fast charging each 12V battery separately, with two inexpensive commercial 15/3 amp smart chargers. Great product functionally, but hideous EMI emissions; they completely obliterate the entire AM radio band. Very limited options for 24V chargers, and big bucks. One of the 12V marine batteries is 3 years old, the other new, so fast charging separately is better anyway. Maintenance charging at 1.5A or less is presently at 24V. If I added 6V to have a 24/30V option, I just add another 15/3 amp charger, which also does 6V, but would revise the maintenance charger, probably to 3 separate 1.5A chargers as well.
My neighbor finally got his welded projector shielding enclosure back yestetrday. MIG welded 1/8" thick steel, 24x30x24", with a waveguide for light, honeycomb vents, deep lapped 3/16 access lid in the rear. Built to my sketches, doesn't look bad though an amateur welding job. Someone didn't get the basic welding class/chapter on gapping and filling joints from the outside of the box and instead it's lapped joints with welding inside and out. Twice the work, not as good for shielding due to discontinuity of shield thickness. Oh well.
I've noticed that the price of EMI shielding products like honeycomb vents and fingerstock or conductive fabric over foam gaskets have doubled in the last 20 years. And lead times have gotten longer, with virtually no one stocking anything. I had to order the honeycomb vents from Holland to get anything in less than 3 months. It seems not too many hobbyists or anyone else are doing serious EMC work.
I ordered an oxy-acetylene cutting/welding rig last week. Got it yesterday, tanks in a couple days. While sold as Neiko made and Victor-type, it's neither; no flashback arrestors in the handle or otherwise. (I ordered them immediately.) I'm going to try my hand at gas welding and brazing, which is zero EMF exposure, but primarily, I have always wanted a cutting torch. I have the fantasy that with a neutral or oxidizing flame, the acetylene won't do me in, used outdoors. I should be able to turn off the acetylene for cutting once started if it does. A respirator is an option, and I also have a fresh air supplied helmet (with remote blower) if needed.