If it's sturdy than you're golden. If not you can add more screw or bolt it down. If you plan on making more/ like building ramps and other stuff regularly grab a miter saw and you can make cuts easy, and angle any bracing. If you need tools check out fathers day sales. Even if you don't have a kid walking around it's a great time to scoop up deals on power tools. I think I bought a decent miter saw for $99 and a drill I need for around
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$50 on different fathers days. Winters here though so shred that thing up and have a good season.
If you land on the pvc where it doesnt have support it could crack if it gets cold where you live, for future rails i suggest having the wood along the whole bottom of the rail
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Looks well thought out though
