Professionally, I cannot recommend any exterior finishes on plywood
holding up w/o a lot of maintenance. The problem isn't so much the
finish applied, as the wood veneer used in the plywood. One needs to
use a wood species that is weather resistant such as redwood, cedar,
teak, cypress, etc. which don't come very economically in plywood
veneers.  Most plywood veneers are interior grades of wood & check,
warp, split, etc. when exposed to the weather, which hammers the
finish. That said, use a marine grade finish if you must use plywood,
& be prepared to refinish every couple of years, or use solid pieces
of the above woods at great expense, lack of sustainability, etc.
Metal/fiberglass panels maybe better suited & lighter weight for
cladding on trailer sides?

YMMV,

Mr. BZ, AIA

On Aug 7, 2008, at 6:31 PM, Mike Elliott wrote:

> Tom Buese may have some suggestions about finishes for plywood that
> can
> actually stand up to weather. Then again, maybe nothing can.
> --
> Mike "Rocket J Squirrel" Elliott
>
>
> On 8/6/2008 5:56 PM Chris S wrote:
>
>> The chassis is a kit from Harbor Freight:
>>
>> http://www.harborfreight.com/cpi/ctaf/displayitem.taf?
>> Itemnumber=42708
>>
>> I bought it on sale for $120, but that was in 2001.  I initially
>> used it to
>> haul a car-top carrier.
>>
>> I had the remainder of the frame welded by a friend to my specs in
>> 2004.
>> They did an outstanding job!  The top section is a box with a
>> hinged lid
>> that bolts on to the original frame.  I did this so I could remove
>> it incase
>> the chassis was damaged.  I used birch plywood for the sides and
>> the lid
>> which took a lot of labor to sand and coat with several layers of
>> Helmsman's
>> "marine" finish.  I  think I worked 30 hours over 2.5 days to get
>> it done
>> before a planned trip.  The finish proved nearly worthless as it
>> did not
>> stand up to weather the way the can says it should.  I plan on
>> installing
>> marine plywood in it this winter.
>>
>> I'll dig up some construction pics this weekend.
>>
>> Chris.
>>
>> 2008/8/6 Jeff Lincoln <magikvw@gmail.com>
>>
>>> Chris,
>>>
>>> I echo Pete's question here. Was this trailer part of a kit you
>>> found and
>>> if so any chance you might point someone towards where you found
>>> that kit?
>>>
>>> That trailer looks about perfect. Pete - it reminds me os Olsen's
>>>
>>> Thanks,
>>>
>>> Jeff
>>> '90 Carat (Grover)
>>> '86 (We call this one Parts)
>>> '78 Bus (Melissa) Patty's Bus
>>>
>>
>>
>>