I tend to agree with the other posters. Pallets could create a moisture problem and add a fair bit of weight especially went they're wet.
A proper roof structure is the best way to protect your 5er, but it wouldn't be cheap and you may or may not have the right to erect a structure. If it's not an option, hopefully you'll be able to keep the trees trimmed back sufficiently. I'm able to store mine at a cousin's farm in an open area away from trees.
2011 Rockwood Signature Ultra Lite 8293SS, 12K Equal-i-zer
2016 Ford F-250 XLT SuperCrew, 6.2L, 4x4, 6'9" bed, 3.73
2010 Rockwood Roo 23SS (2012 - 2014)
2009 Ford F-150 XLT SuperCrew, 5.4L, 4x4, 5'6" bed (2012 - 2016)