Monocoque and Semi-Monocoque servos are just a different form of construction for mecha. Instead of having a skeleton holding it all together, your mecha's hull would bear the weight of it all. It's a multiplier system. These rules are from V-Max #7 volume 2:
Monocoque(X -0.1): Your hull bears all of the weight, with no internal bracing, like an exo-skeleton on a bug. For this negative modifer, your servo's space all go up by +50%. But your Mv goes down my -2, and can never be less than -2 despite all of the other goodies you put in your mecha.
Semi-Monocoque (X -.05): Your hull only bears half, or a small portion of the weight. Unlike Monocoque construction, it has additional internal bracing. For this negative modifer, your servo's space are increased by +25%, and your Mv goes down by -1, and can never be lower than -1.
Original Source: Mekton Bastion Text Archives
Menu
Mekton Z
History
Product Guide
Destinations
MZML
Credits and Disclaimer
R.Talsorian
ARG
mecha.com
Resources
Resources
Mekton Alpha (PDF)
MZ Rules Archive
Project Nemesis
NMMB 7.1
Official Game Sheets
Software
House Rules
Worlds of Mekton Z
Invasion Terra
Starblade Battalion
Mekton Empire
Algol
Virtual Mekton