My h30 hatch adventures
I did mine about 4 years back, I used a Bomar/Gray molded series 900 in black ***update I think the one I used is this exact one, selling for $249
http://shop.hunterowners.com/detail.htm?group=1255&cat=2006, came out nice, I'd have to measure it for size I'm going down there tomorrow ( I bought it from Pompanette but I think they sell them on this site too. ) I oversized it from the previous opening and simply cut a larger square opening where the original was. Also bought the optional "trim ring" installed from below on the overhead, covered the rough opening perfectly, used only the sealing tape Bomar sells, leak free for years now. That part on the deck is flat, unlike the forward hatch which I'm guessing you already contended with. If you did, how'd you tackle that?
I did my forward one for the third and hopefully last time at the same time I replaced the midships hatch. Used the Bomar molded plastic trapezoidal to fit almost perfectly into that crazy raised combing Hunter molded into the deck that one year. Over the years I had twice made crappy looking wood frame hatches, dreading the day I would have to do the glasswork required for a flat bedding there, but I ended up leaving most of the combing in place, just flattening the top port to starboard and laying the new Bomar on top, I used one narrow strip of aluminum painted white to fill in a very small gap at the aft edge, but the job that haunted me since the day the that hilarious one piece molded lexan original cracked and split after only 4 years of service turned out OK. Did you ever see the original?