Hi Yamp
I'd be inclined to position the skids in line with the keel and also lift them so they just take some weight, not as much as the rear roller, maybe 1/2 or 1/3 rd the weight otherwise the boat won't move on or off as you need it too.
Your other option for beach work would have to be the retriever-mate style unit fitted at the rear of the trailer instead of the last roller then you will get good centre-ing both in the water if you drown the trailer and haul it out afterwards with a long rope and also on the beach if you haul the boat on from the sand.
I used to load in the water if the waves were small and then haul straight out by driving along the beach so the boat trailer eventually ended up behind the truck a fair way along the beach.
Cheers
Chimo.
PS Not with my current boat tho.