Hi Flash
Anyone know the best way to do this? All the joints I have seen are for
joining stuff at right angles.

You could use either a scarf joint or a butt joint. Best pictures I could
find http://tinyurl.com/9d5bm

Scarf joint is neater & stronger, but harder to cut. Butt joint is simple,
albeit unsightly. Use plenty of PVA glue on either, water resistant one is
best.

Dave