I am not very familiar with the 2010 Grayhawk, but in my Seneca, I do not think a larger tank would fit in the space provided. What I did was add an extend-a-stay system. All that does is adds a tee into the line where I can hook up an additional external tank when parked. I use a twenty pound tank, but any size tank would work. I chose a twenty pound tank simply for the ease of taking it down to wal-mart and getting it filled or exchanged.
Lee and Diane
2008 Jayco FS36 bunk model/entertaiment center
2009 Jeep Patriat toad
Retired and enjoying new grandson