I have tried it like that (with the side panel off) but I read somewhere else that if a hard drive is at one temperature all the time then it is probably just normal and won't affect the usability of the drive and won't affect speeds.
But what do i know, or i wouldn't be asking on here about this, but right now as im writing this my drive is still at 48c even while playing games (although you said that shouldn't affect the temp as it is working normally and no harder than usual) I have tried with my other drive that is basically dead now and that was fine at about 25-30c and that drive is about 9 years old now (i dont know if that changes anything) sorry im getting off-topic i guess here :/
But overall if its true that temperature dosent affect anything other than it simply being hot to touch although you wouldnt touch it anyway. then i guess its completely fine and i shouldn't be worried one bit.
Currently 252gb/2.72tb free