2 points per meter does seem to be good though, allowing exceptional shots to deal rather more damage to everybody. as for trenches, how much cover does a trench provide in terms of AP? most of the target simply can't be hit by the shell surely? I suppose foxholes might give additional +4 or so?

Try a little higher and look at page 185. Sandbags start at 8, "standard barricades" are 12. That being said, trenches are such an iconic staple of the genre that they might as well be given a place in table 8-4. I'd guess at 12.

It seems a little strange to me that standard barricades are armor 12. That is the equivilent of ordos terminator armor! Sandbags are probably not more protection then master crafted carapace… I think i would halve those values pherhaps, although I suppose you can wear down cover reasonably quickly.. If trenches were classed as cover, could they then be worn down? That's kinda difficult to do without ordinance, but lasguns would be able to do it in theory if they had armor twelve.

@Trentmorten

The difference would be the thickness involved. A sandbag barrier is, what, 40cm thick? Compare that to Carapace which I would not put at more than two or at most three centimetres (ok, it's 40K, so make that 5).

In the same way, a barricade doesn't have to move on its own. While a Tactical Dreadnought must incorporate armour, "muscle" fibers, flexible areas, cogitators, cooling, user interface and lots of other tech-gizmos, a barricade is armour through and through.

I've always thought from what I've seen of their use in TT that Basilisks are used in the same way as British 25 pounders were in the desert, used as artillery but also as direct fire against tanks (or in the 40K universe things like carnefexes and demons and so forth) and sometimes fortifications if the guns could be brought up close enough.  Also if you look at the models for the Earthshaker cannon they look very reminicent of the German 88mm guns from their mounting and gunshield (merging the AA mount and the PaK version gunshield from what I remember). 

To me 2D10 meters deviation would be what you'd get from a direct shot that missed, I've never liked the fact that ordinance and other weapons that have an area effect often if they miss do nothing (by the rules at least, I know many of you like me will have had things happen regardless).  To me a basilisk that fires indirectly should probably deviate this much at least if it hits and should probably deviate more then this in reality, obviously more DoS would bring it down (say a success but no aditional DoS=5D10 meters deviation, with one D10 removed for every DoS? thats me just pulling numbers from my arse so feel free to come up with better ones) with the quality of range finding equipment, gunnery crew, spotters, etc giving bonuses/negatives.

Well this is pretty much a non issue. The current deviation rules from the errata are enough to make sure a basilisk will at least have a fairly significant chance of not murdering the party in the event of a miss. At least now a GM can use the "the squad finds themselves being targeted by basilisk fire" line, and not get incredulous looks from the players who know the GM is outright cheating so as to not murder the party (as previously if they were being targeted, it could never miss).