Windows Production Apache Cluster. Mongrel sleeps

When running production mode on Windows 2003 using Apache and a proxy
balancer mod and mod_rewrite to redirect to the mongrel instances, I
sometimes get a Proxy Error thrown from Apache.

Setup is done according to this guide:

4 Mongrel processes run as Windows Services on high ports (4000+)

VHost entry:

<Proxy balancer://ruby_cluster>

<VirtualHost *:80>
  ServerName ************
  DocumentRoot C:/websites/***********/

  <Directory C:/websites/**********/public/ >
    Options Indexes FollowSymLinks MultiViews
    AllowOverride All
    Order allow,deny
    allow from all

  ErrorLog C:/websites/**********/log/apache_error.log
  LogLevel warn

  CustomLog C:/websites/**********/log/apache_access.log combined

  RewriteEngine On

  # Check for maintenance file and redirect all requests
  RewriteCond %{DOCUMENT_ROOT}/system/maintenance.html -f
  RewriteCond %{SCRIPT_FILENAME} !maintenance.html
  RewriteRule ^.*$ /system/maintenance.html [L]

  # Rewrite index to check for static
  RewriteRule ^/$ /index.html [QSA]

  # Rewrite to check for Rails cached page
  RewriteRule ^([^.]+)$ $1.html [QSA]

  # Redirect all non-static requests to cluster
  RewriteRule ^/(.*)$ balancer://ruby_cluster%{REQUEST_URI} [P,QSA,L]

Now this all works fine. Apache gets hit on port 80 like normal and
redirects its request to one of the 4 mongrel services which will render
the appropriate response.

However when the website hasn't seen traffic in a long while, lets say
roughly 24 hours, the first hit always results in a 502 Proxy Error from

Proxy Error

The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request GET /.

Reason: Error reading from remote server

Refreshing the page will display the ruby generated page correctly

It seems that Mongrel falls asleep or something like that and will react
either too late or with an invalid response when queried by Apache.

Does anyone have any advice on how to counter this problem?