As far as I know, the only thing from TRO 3025 that hasn't been made by RP/IWM is the Repair Facility. I've seen a few Unofficial " 'Mech Repair Bays", though they tend to be made of resin and a bit more expensive than I want to pay for one. The TRO description says there is no "Standard" for them though, so any/all of them could be considered to be "Correct" I guess.
'Mech Repair Bays and 'Mech Hangers have always been the same to me. You need a spot for each 'Mech in your unit, and most units are pretty big. I've seen resin ones done by (I can't remember his company's name, but he is active here on the forum), and they look very nice. And if I just needed the four hangers that his provides I'd be all in, but I need more than that. Actually, a lot more (I guess if I just wanted to use it as a third party 'Mech Repair Bay, like say the old Eire MechWorks before Insta-Tech waved it's magic wand and gave back unlimited technology to the BattleTech Universe, it would work). The old Revell made Robotech ones are nice, but they are OOP and can be just as expensive. What we need it is a cheap way to mass produce the hangers, and ideally have them be connected and expandable. That doesn't leave a lot of options, even when just discussing material cost...
Is anyone familiar with Fat Dragon Games? They do cardstock terrain, mainly for Fantasy miniatures, although they do have a card stock Lost Reich mecha line. You print the product off at home on your printer and assemble as needed. One of their main produces is used to build dungeons and dungeon corridors, which means the stuff is interlocking (but not in a way that can't be undone) and expandable. They already have an E-Z Future set (in their Sci-Fi section) that could be used for a Castle Brian, but it is really scaled for 15mm figures, so some stuff doesn't look right (like control panels with buttons that would take a 'Mech to push). FDG used to have a terrain set called MechBattle City (office towers, power generators, storage tanks, communications dishes and a few other things along with roads that you could turn grid lines on and off), but it was discontinued, I'll assume for lack of interest. I think this would be perfect for building a 'Mech Bay out of. Want two slots, build just two. Need 200, well you might need another pack of paper and an extra glue stick, but sure, you could make the building as big as you'd like. Plus, FDG likes to put all kinds of accessories in their sets, so gantry cranes and other stuff like that isn't out of the question.
I've asked him about doing something like this, and he doesn't seem against it. Where I see the problem at is in sales. If MechBattle City was discontinued for lack of sales (and why discontinue a PDF file!?), then this would be a niche product. I think he would have to know there was some interest before he would even consider a KickStarter for it.
Granted, this wouldn't be a RP/IWM metals product. In fact, it wouldn't even be an officially sanctioned product. But what it would do is give us not just an affordable means of building a large 'Mech Bay, but also an easy one (because it wouldn't need to be painted, just put together).
Anyway... It is just an idea
Caz