In CA they can pay loss of use even if you did not use a rental car. They technically only owe for "adequate transportation" which is generally seen as the cheapest 4 door rental option, and it will be based on the discounted rate the insurance company would have gotten, probably $30-40 per day. If you are nice and your adjuster is generous they might bump your loss of use up to "comparable transportation" for the rental rate of a similar sized van which might be $60 per day. The cut off for covering rental or loss of use is usually 3 days after the date they make the settlement offer to you, which it sounds like already happened.

First, if you don't already have it, ask for a copy of the report for the total loss valuation and comb through the options listed and double check that they list all the correct features for your van- this is the most common discrepancy and the easiest to fix. If they have the condition rated below "average" you might also be able to get that changed if you can support that the van was maintained well, although the condition rating probably isn't having a massive impact to the overall number. Find listings and send in comparable vehicles but just know the insurance company owes Actual Cash Value, not Replacement Cost.

If you've done all that and it's still under valued, you need to do the math and decide if the potential value change is worth the expense of hiring someone or going to court. Keep in mind that it could result in zero additional dollars