Being a true Celt (Irish father, Scottish mother) I have blonde hair, very pale skin and freckles. Out of all us siblings, I tend to tan the easiest though! I've been using sunbeds since December last year and I started with a low-powered bed once a week. At first I would go a little bit pink, then back to white, but after 4 sessions I started to get a little bit of a permanent glow about me. So then I upped to 2 beds per week. My tan didn't really show until end of January though, and even then it was only the people who knew me who spotted that I had a tan!!
I'm now on high-powered beds and use 1 session a week to sustain (not build) my colour. I have a lovely golden tan and people comment on how healthy I look and ask if I've been on holiday.
So you can do it, but it takes a long time with our skin tone. Do you really want to sustain sunbeds for that period of time?