There is a Pearson owners group on the Chesapeake. Not P30 specific, but they welcome P30's.
I do not have specific dimensions for a boom tent. Are you just looking to keep the sun and rain off of people, or are you trying to seal the cockpit?
I built a snow tent this winter that consisted of a 10X12 brown, poly tarp and sections of PVC electrical conduit, with 90-degree elbows.
I cut the conduit to the appropriate length, then zip-tied the conduit to the lifeline stanchions. I fitted the elbows to the ends, to join the port and starboard conduits to form a roof with a peak. This kept the snow sliding off of the roof, instead of piling up and collapsing the tent.
I used a piece of steel conduit as the central spine.
I used one piece of additional conduit on each side, horizontally to join all of the frame pieces for stability.
I just cut everything down by eye, and didn't take measurements. I can measure the pieces and the mainsail cover tonight, I guess and post the dimensions.