Stephen,
I am sure everyone will have an opinion here.
My RMC has the exact same setup as yours. Couple of things to check.
1. Make sure the bottoms arms are in fact Series 2 and are on the right side of the car (ie right and left). The ball joint casting at the end of the wishbone should be angled forward. I have heard cars with these bottom arms on backwards.
2. Check the top wishbones are also the right way round also particularly series one. Make sure all the shims on the top ball joint are all at the front of the ball joint. This helps with caster. I think there has been a discussion post on this previously.
3. Best Caster I could achieve was 3°, if I tried to go further the wheel went too far back in the wheel arch (Didn't look right). I am running with 1° Camber. I can get more camber if needed but I think it is unecessary for the road. 3° Caster works fine for my RMC. Holds tight on the road and does not shift in the bumps. If I went any more I would consider chassis changes different wishbones and then probably power steering.
Other than changing chassis config or grinding out the wishbone support bolt/arm (Not a great idea!!), you can fabrcate new wishbones and make them adjustable both top and bottom giving you ultimate adjustment.
Lowering may help a little but marginal I would think unless your ride height is not correct. Perhaps you should measure ride height of my car when you see it next. I will probably bring it to next meeting.
Cheers
TC