Sounds to me like a temp issue. Maybe it was 300 at the top of the egg but not at your roasting pan. I also think 300 is low for roasting potatoes.
XL BGE, Cold smokehouse, Kamado Joe Jr, Santa Maria pit, Backwoods Chubby, 26.75" Weber custom performer, Blackstone 36" griddle, MAK One Star pellet cooker, 22"WSM, Jumbo Joe, WGA, Smokey Joe
Custom wooden handles for BBQ's made by Marty Leach (oh, that's me)