Accumulated sun damage is no joke, especially among lighter-skinned folks with lighter-colored eyes and hair, although anyone can have this, but the former are far more prone. Sun damage exists at deeper levels of the skin too. You're fortunate to get on this now before it does become much more serious. One way to be scared straight is to see a Visia printout of one's skin which shows what's going on, and will be going on later in life if one doesn't take steps soon to prevent MORE damage. That chemotherapy cream DOES sound heavy-duty - I'm sure your dermatologist had his/her reasons for prescribing. Still, the wearing of a decent facial sunblock IS de rigeur along with a broad-brimmed hat - especially with all the sun you get from hiking. If you don't want to wear sunblock all over, then covering up with tightly-woven fabric is the best thing. Something you can do from the inside although this takes time to take effect and doesn't necessarily replace other sun-protective measures is taking astaxanthin, a very powerful anti-oxidant that has multiple benefits, including that of making skin much more resistant to sun burning and resulting damage, an internal sunscreen if you will. However, it does take several weeks for the astaxanthin to build up in the body to do this, and do do the other stuff that has been suggested for you.
On the topic of facial sunblocks, although they are universally-recommended by dermatologists, in actuality it is not all that easy to find one that one likes. Chemical sunblocks irritate many sensitive skins(I'm one of these), and often purely physical sunblocks are heavy, greasy, and leave a white cast, which depending on one's skin color can leave on looking like Caspar-the-Friendly-Ghost. Often, one has to spend some money to get a decent one, I've found. My HG one right now, although pricey but lasts a long time since I only use it on face and neck is CosMedix Reflect SPF 30 which I wear daily no matter what the weather. It's a physical block, titanium dioxide with anti-oxidants in it, in spray form. At first when I used this I wonder how this could be protective since it felt so light and in spray form besides. But I've been out whole afternoons in reasonably strong sun and gotten no color. Plus it feels very pleasant and hydrating going on the face and doesn't have any toxic stuff in it - a very nice combo of natural and scientific formulation.
Anyhow, best of luck with addressing the sun damage. Let us know how the strong cream treatment is going. Likely while your skin is stressed from this, you will have to use very simple, bland products that are soothing and healing - check with your dermatologist about this, but on the natural side, unrefined shea butter is wonderful.