1977 Layton holding tank question

[Will77]

Hi, I am the proud new owner of a 1977 21' Layton travel trailer. I have gutted the interior and am just about done replacing the floor, but before finishing that up, I am wondering about the grey and black holding tanks. My question is whether I should replace them simply because of age even though they look fine from the outside. They do not leak and appear in good shape. They are both sort of a speckled gray and my guess it that they are some sort of molded poly, no apparent seams. I am planning on replacing the valves and external plumbing, but would love to avoid pulling the tanks. Any thoughts?
Will

[Roosters 67]

Welcome to IRV2 and as far as the tanks, if there are no stress cracks near the mounting rails, and no other obvious damage I say save the money for more important stuff, like upgrading the tank sensors to some thing like seelevel or at least horst tank probes. but just my opinion.

Again welcome to IRV2

Spence

[77Travco]

I would leave them alone if they are not leaking and seem to be ok.