I'm currently getting ready to upgrade about 10 cannons of various flavors. I bought them all with an Anaconda (since they range from Huge to Small), and stored them, which I'll transfer to Sarge when I get there. That said, I usually use the Anaconda for engineering trips. You can fit anything on it that'd fit on any other ship (as far as I saw). So you can just buy lesser class equipment, store it, and then transfer to the engineer.
Currently going around picking up the commodities (Ive got tons of the materials needed). The only drawback, which apparently will be resolved, is that the CMM composites (needed to re-level engineers after "buying" favors*) and Reinforced Mounting Plates (needed for all G5 Overcharged mods), are only available at outposts, thus, no L pads.
So I found a shipyard in a neighboring system, and bought a Type 6, whose sole purpose is to jump one system away and buy the commodities. Transfer back into the Anaconda, and go on my way.
I've got all the commodity locations bookmarked, so it's pretty simple.
For the time being, I'm using a couple of stationed Type 6s for this purpose. They're only about a mil cr each, so it's not that big of a deal. If this next update removes the commodities, I'll just sell them.
But as I'm buying other ships I want to try out (FDL/FAS, etc), I'll keep those around, since a lot of the mods from engineers I like/want, require the same materials/commodities.
*I'm too impatient to try 20 rolls on a single weapon to get lucky and get High Yield and/or Corrosive shell, so I just do the favor thing, then re-level. It takes a little planning, especially if you want to do it a few times (or 6). So I get all the stuff around for G3 and G4 upgrades to get back to G5.
I've spent the better part of the last two months, doing nothing else than Engineer stuff (unlocking them, leveling them all up). There are only two left to unlock, and one requires the Shinrarta pass (Lori, only want the SCB mods)... The other one is Bris, which has nothing I really care about.
I'm actually having a fair amount of fun trying/modding different weapons and combinations. I've got various rapid fire and overcharged pulse lasers, with different side effects on them, same with Multi cannons and Railguns.
You're given 60 storage slots, I think I'm at 40 (still storing a half dozen Shield Boosters, waiting for a ship to put them in), of which probably half are weapons. Once something's modded, it gets transferred back to my "home" base, where I mix and match them on a Python/Anaconda for field testing. If there's something I don't particularly like, it gets re-engineered into something else.
In the last couple weeks, I've gotten really focused on the mods I think are useful, or at the very least, what I think are worth a try. As such, the materials and data collected has been pruned to those that I will need, so when I'm collecting things, if there's something I don't need, I either don't pick it up (mat), or it gets discarded (data).