pla is fine.
I've had birdfeeders and dog crap bag dispensers outside in the english weather for 5 years.
After a couple og years the colour fades, but the plastic is as good as ever.

What people tend to do is misinterpret the term: 'biodegradable'.
Yes pla will biodegrade - BUT only in a hot compost heap, under very specific and extreme conditions. Like deep in a landfill site.
For outdoor applications, it's actually a lot more durable and long lasting than abs.

Just paint it - can't see any real point in the xtc.