The MP limit (paraphrasing) is based on the presence of the DWP/DMP, not the quantity. If I had one in each arm and the torso (as is the current limit for bipedal units), its only -3 MP (Medium) or -2 MP (Heavy/Assault), with exactly 0 converting to 1 MP; it is known that MPs cannot be reduced below Zero in this manner, but there is no cumulative penalty for mounting multiple DWPs...
The reason I bring up DWP limits is this: a player has asked if they could put three (3) Battle Armor Tube Artillery (TacOps p.284) on a single assault-class quad. The claim is that, despite the weight reduction and cutting back drastically on ammo and armor, the construction/build is "legal" because the slot limit has also been satisfied based on the current wording (normally 4 slots reduced to 1 as a DWP; x3 = 3) (TacOps p412-413).
As the GM, I have currently blocked my players BA units from carrying more than 1 BA Tube Artillery per suit Right now, the justification is based on the for BA Tube Artillery having an equipment slot restriction (Body only). ...While it is admittedly not a strong argument, we have agreed to the "head canon" that perhaps the BA Tube Artillery is too bulky of a piece of equipment and [specifically] cannot be mounted in multiples.
We are concerned that someone else will eventually exploit this loophole, and my players agree with me that the current "limitless" approach may be against the spirit of the game.