I can't decide what to take because the warhammer won't ever have much of a mod
It may not have much of a mod, but it does have PPCs and the range/gunnery edge over most units on the board. Are yours ER PPCs? Basically set up your Warhammer and Dan's Awesome together in the woods north of the little 3 hex plateau on the south side of the north map as semi-mobile turrets. Come near us and eat PPC death. Put the rest of the units slightly south in a position to focus fire on the bridge or anything crossing it. Put them down in the canyon at the chokepoint just north of the bridge where anything that wants to draw line of sight has to jump into an exposed position. Set up the lightest/weakest mech with a searchlight on one of the tall plateaus where its search light can illuminate south to the OpFor's starting location. With the spotter back out of range and illuminating/spotting targets that can't reach it back, Everything with LRMs can indirect targets, which should ignore moonless night because you are targeting the hex, IIRC.
The Cataphract has an XL engine, making it more vulnerable, particularly to the strafing attack(s) if they can hit the back. The Vindicators and Cataphract have single ER PPCs, jump jets, and good gunners, making them priority targets. The Highlander is a major threat as well, but the pilot is only a 4 gunner, which will hurt in this kind of a high mod game. The Marauder has a LL instead of one PPC, reducing its damage and range, but improving its heat efficiency. The Stalker is dangerous, but heat limited and will face mod/range issues.
Who are the reinforcement lances? I assume Reaper, but who is the second? If Reaper inserts near the northern plateau of the southern canyon map with a second lance, they coulddo something very similar from the south. Leave a spotter mech on the southern plateau in the woods and just let it illuminate/spot a target. If we work on whittling the force down before engaging in close combat, we should be able to clean up.
There aren't very many places where the convoy can actually escape out of the canyon, so boxing them in with two strong forces that can focus fire should work fairly well.