the pedistal mounts are a good thing,but they if used on a single downrigger puts a lot of sterss on the mounting plate or wherever you mount it to.you got to make sure where you mount it to has enough backing area to handle the stress,and use stanless steel mounting hardware with locking nuts,lock washers and a jam nut also.can never be to carefull with the mounting.the backing plate should be as big as space allows,the bigger the better,spreads the stress out over a larger area.
get a pair of riggers,put them out as far as possible to the back and the sides of the boat.the wider the spread,the less chance of fubars(nasty cut the tangle) out of the lines,and less chance of getting into the prop on turns when running shallow rods.dual fod holders are the way to go,allows you to run sliders,or stack the rods,but increases the chance to get the fubars also.wish i got dual holders with my cannons,but the big jons has duals.
the other thing you can do is go to big jons website,they have a track you mount with pedistals to the deck,then mount the riggers to them,the only drawback is that is is permanent,no removing the track,or pedistals.im not sure but cabelas has the same thing or something similar to it.sometimes you have to make custom mounts to fit the boat,i had to,but get them made out of aluminum,or stainless.
are you going to leave them monted permantly or remove them when not in use?the base/pedistal will be there,the rigger can be removed easy and quickly.
ebay has a section for downrigger/outrigger stuff.some good stuff,but be careful on how much you bid.sometimes things go for more than you can buy it in the store for.bid what YOU want to pay for it right off the bat,then go from there.
P.T.Barnum once said,there is a sucker born every second! and on ebay there is a LOT!