Having done it a few times now, I've realised that you can't take more than a handful of riders in one go along the B2139 up to the A29/A284 roundabout. Climbing Bury Hill on the A29 would be much more preferable if the Gurkha bridge route is too wet.
However, once at the roundabout at the top, the A284 descent to Arundel is my preferred route, and then past Ford as normal, as you have far more space compared with descending the A29 and turning off at Slindon. Having been at the back several times we've gone down the A29, on that first section I've seen numerous very close passes by vehicles, and some riders have been been very lucky not to get taken out.