For a manual penthouse, that would be too much weight.
When I put a 35# solar panel on my PH I found it was very difficult to lift the top. I had to adjust the PH springs to get the top to go up normally.
You could add the rack and solar panels, adjust the PH springs and make it work. But, if you put stuff in the rack (why else would you have it?) then you may not be able to lift the top.
Here is a link to a thread about adjusting the springs:
I suppose you could load it up, drive to your campsite, empty the rack, then lift the top. That should work, since you won't be able to get stuff off the top once the top is up anyway.
Another option is a portable electric penthouse lift. SMB used to sell these, but not anymore. And they are hard to find used - anyone who has one wants to keep it. Sounds like a business oportunity for some enterprising member.