Heat will often mess up drugs, shortening the life expectancy. Some much more than others. Keep them cool. refrigerate if at all possible, will actually lengthen the "use by" date. Many can be kept frozen. Extends the shelf life even further. So, either remove them from the rig, or keep them cold.
We have ours in a small tote that can be easily taken out, or tossed into the 'fridge.
1987 Starcraft Nova tent trailer, purch. '87, sold 8.14
2013 Crusader 290RLT bought new, 8.14
2001 Ford F-250 7.3
A Loving wife and Mason the always dirty dog!