Dynamic URLs and SEO

Hi everyone,

So we have a site that has a filtering system that filters products dynamically using buttons and other options.

We have a couple of issues. First off, the URLs have "[]" brackets. This causes links that are posted on Bbcode websites to break. A link that is given as www.example.com/products?filter1[]=option1&filter1[]=option2

break right after the first "filter" part and before brackets.
***Just like on the forums here.

The links simply are not clickable any more on Bbcode forums which is costing us some traffic.

I have read about the use of special characters in URLs and that they should be escaped like www.example.com/products?filter%5d%5b=option1 which would replace the brackets.

Our filtering system also repeats a filter in the URL which makes it longer like this: www.example.com/products?filter1[]=option1&filter1[]=option2 instead of www.example.com/products?filter1=option1,option2 which makes our URLs longer than needed and not as nice.

I'm wondering if you guys have some advice here. We definitely need to use dynamic URLs with our filtering system. We're toying with the idea of using commas to separate the options and using the "filter" only once in the URL like www.example.com/products?filter1=option1,option2 but commas are also reserved characters so we're not sure what to do.

Our dev says that this would necessitate completely gutting the filtering system and might be over a week of work for him to re-do so this would not be an inexpensive change. If we were to do it, I was wondering what the best way to go would be.

Thank you for your help and advice in advance.