Forgive me if I'm wrong, since I haven't played stock in years, but couldn't you fit all the motors onto 1 blue snapper like so?
(https://gametechmods.com/uploads/images/95961snapperload.png)
With black being the snapper, blue being RADs, red being extenders and green being z-tecs(I thought you were using 2 when I drew this, sorry)
Forgive the ignorance, I've got snapper loading down but I'm not sure on the set up I should be using to get all of the motors onto the snapper.
There are a few ways to do it. I was gonna show you a few but I ended up just building a whole bot instead. Anyway, this is just to show you that it's possible, and how many more weapons you can fit on there if you build everything off the snapper.
(https://gametechmods.com/uploads/images/97882screenshot_16.png)
nah weather it's 4WD or 6WD is mostly inconsequential on a HW popup. The main difference here is that he'll have less weaponry. Ditch the side plows though unless you plan on moving them further forward like so (https://wiki.gametechmods.com/index.php?title=Emerton).
The main thing you need to focus on with popups is size. No, not making it smaller. You need to make the chassis as large as you can and as shallow as you can. Basically you want to have a chassis something like this:
(http://i.imgur.com/msZEvg2.jpg)
Don't worry about having your chassis exposed when you do this, since chassis HP scales with size. Larger chassis means you'll be able to use upward snapping burst motors easier, and they'll act as a srimech.
Right now you have 1600 output from the 2 black batteries, and the 3 DDTs are using 1500 of that 1600. Since spin motors are 100 each, 2 DDTs and 6 HPZ are 1600 exactly. I'd use either that or 3 snapper2's. Battery stats are located here (http://beetlebros.gametechmods.com/ra2stats.htm).