Paul,

You should be okay with your 50lb. kayak.  I carry two kayaks and a surfboard
on my Yakama rack.  One of my kayaks is 19ft. long (Surfski).  I have carried
all three at the same time down the hiway for 600 miles straight at 65-70
mph.  The sideloader brackets come with a large backing plate.  I read
somewhere that it also helps to use large washers with the backing plate,
which is what I did. One thing I do with my kayaks, if I am going any
distance at high speeds, is put a strap across the bow porton of the kayaks
and through the tie-downs on the luggage rack area above the driver/passenger
area.  This seems to take some of the stress off the wind force trying to
pull up the pop-top and also takes some stress off of the racks themselves.

Good luck,

Bryan Jones
'91 Westy
'98 Beetle