How much oil leaks out over night or when you park the truck? If too much, I would be pulling over and checking the oil if you do the drive. You should be ok. Try the above mentioned ideas and if they don't work, then get a new cover. If you want a used one, I have some or try the for sale and wanted sections. Isn't working on your rig fun??
Good luck
Jeff

It's all good!
83 Shortbed stepside lots of mods
82 Shortbed fully restored
85 Shortbed daily driver
88 4-runner-Wife's daily driver